The present invention relates to a cell for measuring the amount of insoluble particles in a fluid, to a device comprising such cell as well as to a method for measuring the amount of insoluble particles in a fluid. The invention also relates to the application of this method and to the use of the device according to the invention in the study of oxidation stability of oil middle distillates, in the study of the antioxidant capacity of an additive of petroleum products and in the determination of the amount of asphaltenes present in a petroleum product sample.
Conventionally, oil middle distillates are oil distillates which have a boiling point substantially above 175° C. and which are 90% vaporized at a temperature below 370° C. Kerosine, gasoil or domestic fuel oil (DFO) notably belong to these oil middle distillates. In order to determine the storage stability of these fluids, the standardization bodies, ASTM for the United States and AFNOR for France, have respectively defined under references ASTM D 2274 and NF EN ISO 12205 (classification index NF M07-047), an oxidation stability test for middle oil distillates. This test in a first step consists of filtering a fluid sample so as to determine the amount of insoluble particles, called “existing insolubles”, actually present in this state in the fluid.
In a second phase, the fluid sample is placed in an oxidation cell. In this cell, the fluid is heated to a temperature of 95° C. for 16 hours. At the same time, oxygen gas is injected into the sample continuously. After having been cooled, the fluid sample is poured on a filter so as to retain the non-soluble particles then present in the fluid, these particles being called in the NF standard “filterable insolubles”. The amount of filterable insolubles is finally determined by weighing the residue present on the filter.
In a third step, the oxidation cell is rinsed by means of a trisolvent—usually consisting of toluene, methanol and acetone. The trisolvent is then evaporated. The residue obtained after this evaporation consists of non-soluble particles called in the NF standard “adherent insolubles”. The amount of adherent insolubles is determined by weighing the mass of the residue after evaporation of the trisolvent. The total amount of insoluble particles or “total insolubles” allows determination of whether the tested liquid has satisfactory stability towards oxidation. This amount of total insolubles is obtained by adding the amounts of filterable insolubles and adherent insolubles.
Although actually allowing determination of the stability towards oxidation of middle oil distillates, this test has the drawback of being long, complicated, requiring a significant volume of sample (generally 350 mL) and having poor repeatability. Further, significant operator time (of the order of 3 h) is required for applying this method and a large amount of organic solvent is notably handled for proceeding with the cleaning of the required glassware. Further, with the known method, it is not possible to obtain information concerning the kinetics for formation of the insoluble particles.
From EP 1 751 518 in the name of the applicant, a device is known for measuring light in a liquid by inserting into the liquid at least one probe operating by indirect transmission—reflection—of the light in the fluid. EP 1 751 518 also describes a method for measuring, by means of the measuring device, the flocculation threshold of a colloidal medium by staged addition of apolar solvent, a drop in the transmitted light in the measuring device expressing occurrence of flocculation. However, in the state in the art, there are no available means for automating the oxidation stability test of oil middle distillates, as presented above, nor for reducing the operator time or the use of organic solvent.
Moreover, DE-A-43 12 112 discloses a device for measuring the soot concentration of flue gases. This device comprises a probe provided at one end with a measuring component containing a housing. This housing is intended for receiving a filter for measuring soots, when the measuring component is in its measuring position. The measuring component also comprises, in the area of the housing, an optical measuring device for determining the amount of soot. This optical measuring device may emit a light intensity and measure the light reflected by the measuring filter.
EP-A-1 775 571 teaches a device for monitoring the particle burden of a fluid. The monitoring device includes a measuring chamber with an inlet and outlet for the fluid. A filter is placed in the measuring chamber, between the inlet and the outlet, for filtering the particles. An illumination device is positioned in the measuring chamber for illuminating the filter. An image recording device is also positioned in the measuring chamber for capturing images of the filter.
DE-A-19 11 656 describes a device for monitoring the ageing of oil for conveying heat in a circuit. The device comprises a straight conduit inside which a filter is positioned. The filter is positioned so as to be crossed by the oil. A light source is arranged on the inlet side of the straight conduit. The light source emits light which crosses the filter. A photovoltaic cell is arranged on the outlet side of the straight conduit. A measuring apparatus is connected to the photovoltaic cell in order to determine the extinction level of the light beam which has crossed the filter. Finally, U.S. Pat. No. 5,715,046 teaches a method and a device for determining the stability of an oil by measuring the light intensity reflected by the surface of the oil when an asphaltene-based liquid flocculant is added to the oil.
The object of the present invention is to provide a device and a measurement method which at least partly overcomes the aforementioned drawbacks. More particularly, the invention is directed to providing a measurement device capable of automatically determining the amount of insoluble particles in a tested liquid. The invention is also directed to providing a measuring cell adapted so as to be applied in the device according to the invention, the measuring cell allowing determination of the amount of insolubles in the tested liquid.
The present invention proposes a cell for measuring the amount of insoluble particles in a fluid comprising:                a duct passing through the cell,        a filter intended for retaining the particles contained in the fluid, the filter being positioned in the duct,        an emitter adapted for emitting an electromagnetic beam directed towards the insoluble particles concentrated on the filter, and a receiver adapted for receiving the electromagnetic beam emitted by the emitter (52) and reflected by the insoluble particles concentrated on the filter.        
According to embodiments of the invention, the measuring cell comprises one or more of the following optional features, taken alone or as a combination:                the electromagnetic beam is a light beam selected from the group comprising an infrared beam, a near infrared beam or an ultraviolet beam;        the emitter is formed by at least one light-emitting diode;        the receiver is selected from the group comprising a light emitting diode and a photodiode;        the filter is made in a material selected from the group comprising polymer-based plastic material such as nylon, nitrocellulose and glass fiber;        the filter has a porosity comprised between 0.1 and 2 μm and preferably between 0.5 and 1.5 μm;        the measuring cell comprises a sensor for measuring the temperature of the fluid;        the measuring cell comprises screen-forming means positioned on the direct path, between the emitter and the receiver, of the electromagnetic beam; and        the incident beam forms with an axis perpendicular to the filter an angle comprised between 45 and 80° and preferably between 60 and 80°.        
The invention also relates to a device for measuring the amount of insoluble particles in a fluid including:                a measuring cell according to the invention as described hereinbefore in all its combinations,        a container adapted for containing a fluid sample to be tested, a circuit for circulating the fluid between the container and the measuring cell, and        means for circulating the fluid in the circuit.        
According to embodiments of the invention, the measuring device comprises one or more of the following optional features, taken alone or as a combination:                the measuring device comprises a duct for injecting gas into the sample;        the device further comprises means for heating the sample;        the device comprises a sensor for measuring the temperature of the sample;        the device comprises a heat exchanger between a section of the circuit located upstream from the measuring cell and a section of the circuit located downstream from the measuring cell;        the device comprises a sensor for measuring the fluid flow rate in the circuit;        the device comprises a pressure sensor located upstream from the measuring cell; and        the measuring device further comprises a computer adapted for receiving information from the emitter and/or the receiver and/or the temperature sensor of the cell and/or the temperature sensor of the sample and more generally from any system for physical measurements positioned in the device, for sending as a response control signals to the different constituents of the device, such as the means for circulating the fluids, and/or for example to the emitter and/or to a display device.        
The invention also relates to a method for measuring the amount of insoluble particles in a fluid comprising at least the following steps of:                concentrating the insoluble particles by filtering the fluid;        determining the amount of the particles from the measurement of the absorption of electromagnetic radiation by the concentrated particles, the measurement of the absorption being conducted by comparing electromagnetic radiation incident on the concentrated particles and the electromagnetic radiation reflected by the concentrated particles.        
According to alternatives of the invention, the measuring method includes one or more of the following optional features, taken alone or as a combination:                the fluid is continuously circulated between a container and a filter adapted for filtering the insoluble particles;        gas is injected into the fluid contained in the container;        the injected gas is oxygen;        the determination of the amount of the particles is conducted continuously;        the fluid contained in the container is heated;        the intensity of the emitted electromagnetic radiation is maintained constant; and        the intensity of the reflected electromagnetic radiation is maintained constant.        
The invention also relates to the use of the measuring cell according to the invention or of the measuring device according to the invention for measuring the oxidation stability of oil middle distillates by determining the amounts of insolubles contained in the distillate. The invention also relates to the application of the measuring method according to the invention to the measurement of the oxidation stability of middle oil distillates by determining the amounts of insolubles contained in the distillate. The invention also relates to the use of the measuring cell according to the invention or of the measuring device according to the invention for determining the amount of asphaltenes present in a petroleum product sample.
The invention further concerns the application of the method according to the invention to the determination of the amount of asphaltenes present in a petroleum product sample. The invention also relates to the use of the measuring cell according to the invention or of the measuring device according to the invention for measuring the antioxidant capacity of petroleum product additives. The invention finally concerns the application of the measuring method according to the invention to measuring the antioxidant capacity of petroleum product additives.